Acoustical Physics最新文献

Acoustic physics problems describing the propagation of acoustic effects or associated flows rely on hydroaeromechanic equations, in particular, on Navier–Stokes equations containing the vector Laplacian of the velocity of a liquid or gaseous medium. One of the most commonly used coordinate systems is spherical. The article discusses a fundamental misprint in “Fluid Mechanics” by L.D. Landau and E.M. Lifshitz (Course of Theoretical Physics, Vol. VI), which has been replicated up to the sixth revised Russian edition of 2021 and which also made it into the English version of the course published by Pergamon. It concerns the Navier–Stokes equation in spherical coordinates (15.21), which describes the r-component of the vector Laplacian. The typo migrates to secondary publications and can complicate theoretical studies related to application of the Navier–Stokes equations, which the author of this note has personally encountered. The r-component of the vector Laplacian is derived in detail from general principles to show what the corresponding Navier–Stokes equation should look like and that the typo is indeed present. In addition, more compact equivalent forms of the Navier–Stokes equations in spherical coordinates are proposed.

Many real liquids contain solid inclusions of various sizes in addition to the liquid phase itself. These inclusions influence the propagation of acoustic waves. Such acoustic wave parameters as absorption and speed of sound propagation depend on the size and concentration of particles. For some multicomponent systems, acoustic parameters can be described quite well using Urick’s proposed theory. In this study, the dependences of the absorption coefficient and speed of sound are obtained for an agarose gel suspension with talc particles and for suspensions with silica particles. Experimental attenuation spectra in different suspensions were compared with theoretical calculations of the Urick model. The dependences of acoustic absorption and speed of sound on concentration in suspensions with different particle sizes were obtained. The comparison results showed that the Urick model satisfactorily describes the absorption in various suspensions at particle concentrations φ < 20%.

The study theoretically evaluates the capabilities of ray-tracing and diffraction-based aberration-correction methods, which are used in noninvasive neurosurgery for focusing high-intensity ultrasound through the skull bones at various depths in the human brain. The analysis is based on using head computed tomography (CT) data of skulls with various geometric characteristics from an anonymized set of eight patients. The transducer is a mosaic 1 MHz phased array shaped like a spherical bowl with a radius of curvature and a diameter of 200 mm, and fully-populated, 256-element layout. In the ray-tracing method, aberrations were corrected by calculating the phase shift along the rays emanating from the target point to the centers of the elements. In the diffraction-based method, calculation of the Rayleigh integral was combined with a pseudospectral numerical method for solving the wave equation in an inhomogeneous medium, implemented in the k-Wave software package and used for aberration correction and ultrasound focusing simulations. It is shown that the strongest field distortions are observed for skulls with more pronounced variations in bone thickness. Compared with the ray-based method, the diffraction-based method provided higher focusing efficiency and enabled aberration correction at shallower depths in the brain.

The paper presents the results of calculating of sound diffraction by screens of various shapes, performed using the finite element method (FEM) developed by the authors in the Bubnov–Galerkin formulation. The calculations were verified on problems with an exact solution (diffraction by a cylinder, a segment, and a sphere), and the results of experimental validation of calculations of sound diffraction by a rectangular screen, performed using the maximum length sequence method, are also presented. The article was prepared based on materials of a report at the 10th Russian conference “Computational Experiment in Aeroacoustics and Aerodynamics,” September 16–21, 2024, Svetlogorsk, Kaliningrad oblast, http://ceaa.imamod.ru/.

Based on the hot-wire method for studying the fluctuations of compressible flows, the issues of determining the acoustic characteristics of the flow in the test sections of wind tunnels at transonic and supersonic speeds are considered. It is shown that for supersonic flows, in addition to the Mach waves described by Kovasznay, generated by stationary sources of disturbances on the walls of the test sections, and Mach waves generating the most intense fluctuations, distributed and moving in a supersonic turbulent boundary, described by Laufer, there may be Mach waves, the sources of which are sounds, as well as a turbulent boundary layer. Using the hot-wire approach, it is possible to determine the characteristics of each type of these waves and their source. It is also established that simple sound waves can be produced by the turbulent boundary layer and penetrate into the leading part from sources launched in the prechamber of the wind tunnel to the critical section of a Laval nozzle. In high-subsonic-speed wind tunnels, acoustic disturbances are produced from sound waves identified by intensity, direction and spectral composition using developed methods of thermal anemometry. The characteristics of acoustic disturbances (intensity, direction, location of sources) determined using the hot-wire method allow them to be purposefully preserved or reduced, or their influence on phenomena under investigation can be taken into account. The article was prepared based on the materials of the report at the 10th Russian conference “Computational Experiment in Aeroacoustics and Aerodynamics,” held September 16–21, 2024, in Svetlogorsk, Kaliningrad region (http://ceaa.imamod.ru/).